Work during the next year will focus on (1) defining the amino acids to which selenocysteine in GSH peroxidase is attached and the sequence of amino acids around it in the polypeptide chain; (2) purifying GSH peroxidase and other Se-containing proteins by HPLC; (3) characterizing Se-GSH peroxidase in rat kidney and lung and determining whether Se is present as selenocysteine; (4) studying GSH peroxidase in a variety of species and tissues; (5) determining whether other Se-containing proteins contain selenium as selenocysteine; (6) studying protection afforded by GSH peroxidase to RBCs exposed to peroxidizing microsomes prepared from Se-deficient rats; and (7) determining whether GSH peroxidase will inhibit lipid peroxidation in vitro in other reaction systems that contain purified liver microsomes.